Spectroscopy of the heavy helium isotope 7He
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Three narrow (Γ ≤ 0.5 MeV) low-lying states of 7He with excitation energies of 3.2(1) MeV, 4.9(2) MeV and 6.65(15) MeV are observed simultaneously for the first time in reactions of the absorption of stopped π−-mesons 11B(π−,pt)7He and 11B(π−,dd)7He. No indications of the existence of a level in the area of E x ∼ 1 MeV are found. Highly excited 7He states with parameters E x = 19.6(3) MeV, Γ = 1.7(4) MeV and E x = 25.2(6) MeV, Γ= 4.8(9) MeV are observed.
KeywordsExcited State Excitation Energy Resonant Energy Distri Butions Neutron Rich Isotope
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